High-temperature turbine casing arrangement



April 1949- c. w. ElZsToN 2,467,818

HIGH-TEMPERATURE TURBINE CASING ARRANGEMENT Filed NOV. 29, 1947 2Sheets-Sheet 1 Fig I.

' Inventor: Charles W E lat on.

I His Attorne s.

li atented Apr. 19, 194% grate PATENT HIGH-TEMPERATURE TURBINE CASINGARRANGEMENT New York Application November 2t, 1947, Serial No. 788,884

The present invention relates to double casing, high temperature elasticfluid turbines. More particularly it relates to a method of andarrangement for maintaining the outer casing of a double casing, hightemperature, elastic fluid turbine at a relatively low temperature.

Since a high thermal efliciency can be attained in a steam turbine byutilizing a high temperature, high pressure fluid operating medium,present day turbines are being designed to accommodate highlysuperheated steam over 1000 F. However, the design of such turbinespresents many problems, one of the most important being the selection ofmaterials for the rotor, casing, buckets, etc.

There are three main factors to consider when selecting materials to beused in a high temperature, high pressure elastic fluid turbine. Thesefactors are the rupture strength, creep strength, and metallurgicalstability of a material, The first of these, rupture strength, isconcerned with the pressure to which a material will be subjected.Therefore it is conceivable that nearly any one of the standard,inexpensive materials could be thickened to a degree such that it wouldbe able to withstand any pressure within reasonable limits. However, thecreep strength and metallurgical stability of any material are primarilyfunctions of the temperature to which the material may be subjected.Nearly all inexpensive low carbon steels ordinarily used for steamturbines have very low creep strength when subjected to temperatures ofthe order of 1050 F. Furthermore, nearly all are metallurgicallyunstable at such temperatures; that is the carbon contained in the steelprecipitates along the grain boundaries causing a phenomenon known asgraphitization which reduces the allowable working stress of the steelto a point which is far below the stresses encountered in present-dayturbines. Therefore, it may be seen that the creep strength andmetallurgical stability factors place very definite limitations on theselection of high temperature materials for steam turbines and the like.

Special austenitic materials such as the socalled cobalt ascaloy" and18-8 chrome-nickel steel have high creep strength and aremetallurgically stable at temperatures of the magnitude described, butthe cost of such materials is' very high when compared with the cost ofstandard steels such as those of the chrome-molybdenum-vanadium typeordinarily used for they casings, rotors, etc., of steam turbines. Thoseparts of a turbine which directly contact the high 5 Claims.

temperature steam would necessarily have to be constructed from theseaustenites. They in-- clude the inner casing, the buckets of the firstfew stages where temperature conditions are most severe, and possiblythe rotor in high speed machines where the shaft and bucket-wheels areintegral. In addition, the outer casing would ordinarily have to be castfrom the austenites also because it has been found that with the designsnow in use, radiant heat from the inner casing causes the outer casingto assume a temperature of only 15-25 degrees below that of the innercasing.

It is well known that by decreasing the normal working temperature ofchrome-molybdenum steel, for instance from 1050 F. to 900 F. the creepstrength for an allowable creep rate .may be increased to about fourtimes its former value, and what is more important, the steel at 900 F.will be metallurgically stable. Since in this temperature range thecreep strength increases rapidly as a function of decrease intemperature and the transition from metallurgical instability tometallurgical stability occurs, readily available inexpensive materialscould be substituted for the high cost austenites which would ordinarilybe required for the outer casing of a high temperature elastic fluidturbine provided the outer casing is maintained at a temperature suchthat the creep strength exceeds the maximum working stress and thematerial is metallurgically stable. This invention provides anarrangement which permits the substitution of inexpensive materials forhigh cost materials which ordinarily would be required in a doublecasing high temperature elastic fluid turbine.

Accordingly, an object of the invention is to provide an improved methodof and arrangement for limiting to a preselected value the temperatureof the outer casing of a double casing high temperature elastic fluidturbine.

Another object is to provide in a double casing high temperature elasticfluid turbine, means for maintaining safe allowable stresses in an outercasing, cast from standard low cost materials.

A further object is to provide a novel arrangement for cooling theforward end portion of the shaft and surrounding structure in a hightemperature elastic fluid turbine.

Still another object is to provide in an elastic fluid turbine means forthe quick disposal of the high temperature packing leakage.

Other objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawings in whichFig. 1 is a longitudinal sectional view of an elastic fluid turbineembodying the invention; Fig. 2 is a radial sectional view taken on theplane 2-2 of Fig. 1 and Fig. 3 is a fragmentary sectional view taken onthe plane 3--3 of Fig. 1.

Referring now to the drawings, a multi-stage elastic fluid turbineincludes an outer casing 2 enclosing an inner casing 3 with an annularchamber 4 defined therebetween. Inner casing 3 is preferably constructedand arranged to include one or more separate sections 3a so that anannular fluid extraction gap 5 is defined between the sections. As iscustomary, outer casing 2 includes upper and lower halves having flangeportions 6,"|, (Fig. 2) while inner casing 3 includes upper and lowerhalves having flange portions 8, 9. Flange portions 6, 1 and 8, 9 areconnected to form joints by a plurality of suitable threaded fasteningsIO, M respectively. Inner casing 3 is supported within outer casing 2 bya plurality of radially projecting extensions |2 formed on flange 9 ofthe inner casing which engage recessed portions l3 formed in flange I ofthe outer casing.

Inner casing 3 is centered within outer casing 2 by means of a pluralityof radially outward projecting tongued keys H which are arranged to formradial clearances with radially inward projecting grooved keys |5 formedon the inner surface of outer casing 2. These keyed portions permit evenradial expansion of inner casing 3 with respect to outer casing 2 sothat the two casings are maintained substantially concentric for alloperating conditions of turbine Similarly, the relative axial movementof inner casing 3 is permitted by axially outward extending tongued keysl6 formed on the "forward end of easing 3 which are adapted to engageaxially inward projecting grooved keys I! formed in outer casing 2.

In the present instance, it is preferred to have the turbine inletvalves (not shown) housed in a separate casing and placed at some pointexternal of the turbine (such as in front of the turbine) rather thanhave the valves mounted on outer casing 2. Inlet conduits l8 communicatethe inlet valves with elastic fluid inlet ports I9, defined by thebossed portions 2|, 22 circumferentially spaced about casings 2, 3respectively as shown in Fig. 2. Eeach conduit |8 has a separate endportion 23 and may be secured thereto by weld or other suitable means.Formed integral or by weld to conduit end portion 23 is a flexibleaxially extending flange 24 having a radially projecting bolting ring 25which is secured to casing 2 by suitable threaded fastenings 26. Inorder to distribute the bolting stresses evenly throughout ring 25, acollar 21 may be interposed between ring 25 and the head portions ofthreaded fastenings 26. The end portion 23 of conduit I8 is secured ininlet port 20 by means of a slip joint 28 which may be any one ofseveral known types, the details of which are not considered material tothe present invention.

Inlet port 20 communicates with a first stage nozzle ring 29 having aplurality of circumferentially spaced nozzle partitions 30 and issecured by suitable fastening means (not shown) to casing 3.

A rotor indicated generally at 3| is supported within casing 3 by meansof suitable bearings (not shown) and comprises a shaft 32 having aplurality of bucket-wheels 33 which may be formed integral with shaft32. Circumferentially spaced around bucket-wheels 33 and secured theretoare a plurality of buckets 34 enclosed by bucket covers 35. Stationarydiaphragms 36 in the form of discs containing a plurality of blades 31forming nozzle passages are supported in cas- 5 ing 3 and are associatedwith wheels 33 for directing elastic fluid to the respective bucketannuli.

Formed in casings 2, 3 are labyrinth packing seals 38, 39 respectivelywhich form close clearances with shaft 32 thereby resisting the flow ofelastic fluid axially outwardly along the shaft. Such leakage can not beentirely prevented so that the portion of high temperature operatingfluid which leaks outwardly between shaft 32 and seal 38 will becollected in an annular groove 40 provided in casing 3 adjacent seal 38.The hot fluid thus collected will pass through conduits 4| (Fig. 2) toaxially extending, open-end extraction conduits 42 provided in chamber 4beneath inner casing 3. For reasons which will be apparent from adescription of the operation of the invention given hereinafter,conduits 4| extend axially into the open ends of conduits 42 and theouter diame ter of the former is smaller than the inner diameter of thelatter. As shown in Fig. 1 and more 25 particularly in Fig. 3,extraction conduits 42 communicate with a single radially outwardlyprojecting conduit 43 within a bossed portion 44 formed on inner casing3. Conduit 43 extends through a bossed portion 45 formed on outer cas-30 ing 2 and communicates with a suitable heat reclaiming device such asa boiler feedwater heater (not shown).

During operation, extremely high temperature elastic fluid such as steamfrom a separate valve 35 chest (not shown) enters the turbine throughconduits l8 and inlet ports 28 to the first stage nozzles 30 and thenceflows axially through the respective buckets 34 and nozzles 31 impartingrotational energy to the rotor 3|. In traversing 40 the flow paththrough buckets 34 and nozzles 31, substantial pressure and temperaturedrops are experienced by the steam so that by the time it reachesbucket-wheel 33a adjacent extraction gap 5, its temperature is very coolrelative to the hot steam entering the turbine. Since the "forward endof chamber 4 is in communication with the open ends of extractionconduits 42 and conduits 42 in turn communicate with a suitable heatreclaiming device, the pressure of which is considerably lower than thatof the cool steam at wheel 33a, a portion of this cool steam will beextracted through gap 5 to chamber 4 and will flow toward the forwardend thereof to conduits 42 as indicated by the arrows in Fig. 1. Infollowing this reversed flowpath in chamber 4, the cool extraction steamexerts a substantial cooling or temperature limiting effect on outercasing 2 and other appurtenant structure adjacent chamber 4,particularly in that area surrounding steam inlet conduits l8 where themost serious temperature conditions are encountered.

Meanwhile, the high temperature leakage steam throttling through seal 38with an accompanying relatively small decrease in temperature collectsin groove 40. Seal 38 and the entrance annulus area between conduits 4|and 42, depending upon the relative magnitude Of the flow of elasticfluid through conduits 4| and conduits 42, can be proportioned so thatthe pressure drop experienced by the high temperature steam throttlingthrough seal 38 is greater than the pressure drop experienced by theoperating steam in passing from the first stage nozzle 30 to wheel 33a.Thus the relatively cool extraction steam in chamber 4 will be at apressure slightly greater shown).

than that of the high temperature packing leakage collected in groove40. Because of this, the

high temperature steam in groove 40 is prevented from flowin axially tothe left through seal 38a (Fig. 1) to chamber 4 where it would exert ahighly undesirable heating effect on the cool extraction steam andcontiguous structure such as the outer casing 2, shaft 32, and bearings(not Instead, all of the steam in groove 40 will pass through conduits4| to conduits 42 where it mixes with and appreciably raises thetemperature of the cool extraction steam entering through the open endsof conduits 42 from chamber 4. The mixture then passes out of theturbine through conduit 43 to the above-mentioned heat reclaimingdevice. As a safety precaution, a bypass conduit 43a containing valve43b is connected at its upstream end to conduit 43 as shown in Fig. 1.conduit 43a may be connected to any medium of lower pressure such as alower pressure stage of turbine I, the turbine exhaust or to anotherheat reclaiming device. Thus during normal operation, valve 43b may beclosed and the steam in conduit 43 passes to the heat reclaiming deviceconnected thereto. If, however, the heat reclaiming device should becomeinoperative, valve 43b would be immediately opened and the steam inconduit 43 would bypass through conduit 43a to a medium of lowerpressure thereby ensuring the continuous and uninterrupted flow ofcooling steam in chamber 4. 7

It has been found that if a double casing steam turbine having an inletsteam temperature of the order of 1050" F. is cooled in accordance withthe above-described method, the outer casing may be maintained at atemperature of the order of 900 F. thus permittin the use of ordinarysteels. If it is desired to maintain the outer casing at a still lowertemperature, radiation shields 45, 4? may be provided in chamber 4 asindicated in Fig. 1, and the relatively cool extraction steam caused toflow between the shields thereby exerting an appreciable temperaturelimiting effect on outer casing 2. The degree of this temperaturelimiting effect is dependent to a certain extent upon the velocity ofthe extraction steam flowing between the shields, which in turn isdependent upon the relative positions of the two shields. It will beobvious that one of the radiation shields may be omitted and theextraction steam caused to flow between a single shield and outer casing2. Here again the temperature limiting effect exerted by the coolextraction steam on outer casin 2 is dependent to a degree upon thevelocity of the extraction steam while the velocity is dependent uponthe position of the shield relative to outer casing 2. The exactposition of shields 46, 41 of Fig. 1 is not considered material to anunderstanding of the present invention sinceanyone reasonably skilled inthe theories of heat transfer may readily calculate the shield positionsnecessary to maintain a preselected outer casing temperature, the valueof which may range between the temperature of the inner casing 3 and thetemperature of the fluid in chamber 4.

Thus it will be seen that this invention provides an improved method ofand arrangement for limiting the temperatures of the outer casing andthe forward end portion of the shaft of double casing elastic fluidturbines thereby permitting the use of ordinary low-cost materials forincreased operating temperatures.

While a particular embodiment of the inven- The downstream end of.

- be obvious to those familiar with the art that various changes andmodifications may be .made without departing from the invention, and itis intended to cover in the appended claims all such changes andmodifications as come within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an extraction type elastic fluid turbine for elevated temperaturesand pressures having a bladed multi-stage rotor supported in an innercasing carrying stationary blades and surrounded by a spaced'outercasing, one or more concentric radiation shields supported in theannular space between said inner and outer casings, conduit means forsupplying motive fluid at high temperature and pressure to one end ofthe inner casing, first labyrinth shaft sealing means at the highpressure end of the inner casing, second shaft seal meansat the adjacentend of the outer casing and forming an annular chamber with said firstseal, walls defining passages for circulating comparatively cooler fluidfrom a low pressure stage of the rotor between the radiation shields andsaid inner and outer casings to said annular chamber, first extractionconduit means for withdrawing motive fluid from said low pressure stage,said first conduit means having an open end portion located between theinner and outer casings and adjacent the high pressure end of the innercasing, and walls defining second conduit means adapted to receiveleakage and cooling fluid at an intermediate region of said first shaftseal, said second conduit being constructed and arranged to dischargesaid fluid into the open end of said first conduit whereby substantiallyall of the high temperature leakage in said first shaft seal is removedto the extraction conduit. I

2. In an extraction typeelastic fluid turbine for elevated temperaturesand pressures having a bladed multi-stage rotor supported in an innercasing carrying stationary blades and surrounded by a spaced outercasing, conduit means for supplying motive fluid at high temperature andpressure to one end of the inner casing, first labyrinth shaft sealingmeans at the high pressure end of the inner casing, second shaft sealmeans at the adjacent end of the outer casing and forming an annularchamber with said first seal, walls defining passages for circulatingcomparatively cooler steam from a low pressure stage of the rotorbetween the inner and outer casing to said annular chamber, firstextraction conduit means for withdrawing motive fluid from said lowpressure stage, said first conduit means having an open end portionlocated between the inner and outer casings and adjacent the highpressure end of the inner casing, and walls defining second conduitmeans adapted to receive leakage and cooling fluid at an intermediateregion of said first shaft seal, said second conduit being constructedand arranged to discharge said fluid into the open end of said firstconduit whereby substantially all of the high temperature leakage insaid first shaft seal is removed to the extraction conduit.

3. In an elastic fluid turbine for elevated temperatures and premureshaving a bladed multistage rotor supported in an inner casing carryingstationary blades and surrounded by a radially spaced outer casing, thecombination of ings, conduit means for supplying motive fluid at hightemperature and pressure to one end or the inner casing and means forcirculating comparatively cool motive fluid from a low-pressure stage ofthe turbine through the passages formed by said inner and outer casingsand the radiation shields. whereby the transmission of heat from saidinner casing to said outer casing is reduced.

4. In an elastic fluid turbine for elevated temperatures and pressureshaving a bladed multistage rotor supported in an inner casing carryingstationary blades and surrounded by a radially spaced outer casing,conduit means for supplying motive fluid at high temperature andpressure to one end of the inner casing, walls defining passages forcirculating comparatively cooler steam from a low pressure stage of therotor between the inner and outer casings, at least one extractionconduit means having an open end portion located between the inner andouter casings and adjacent the high pressure end of the inner casing,said extraction conduit being adapted to receive through the open endportion thereof said cooler steam.

5. In an elastic fluid turbine having a bladed multi-stage rotorsupported in an inner casing carrying stationary blades and surroundedby a radially spaced outer casing, the combination of one or moreradiation shields supported in the annular space between said inner andouter casings, conduit means for supplying motive fluid at hightemperature and pressure to one end of the inner casing, walls definingpassages for circulating comparatively cooler steam from a low pressurestage of the rotor between the radiation shields and the inner and outercasings, at least one extraction conduit means having an open endportion located between the inner and outer casings and adjacent thehigh pressure end of the inner casing, said extraction conduit beingadapted to receive through the open end portion thereof said coolersteam.

CHARLES W. EISTON.

No references cited.

